Its major clinical symptom is the development of cataracts during the first weeks or months of life, as a result of the accumulation, in the lens, of galactitol, a product of an alternative route of galactose utilization.

Some studies have suggested that, depending on milk consumption later in life, heterozygous carriers of galactokinase deficiency may be prone to presenile cataracts at 20–50 years of age.

The only known symptom in affected children is the formation of cataracts, due to the production of galactitol in the lens of the eye.

[citation needed] The human GALK1 gene contains 8 exons and spans approximately 7.3 kb of genomic DNA.

The GALK1 promoter was found to have many features in common with other housekeeping genes, including high GC content, several copies of the binding site for the Sp1 transcription factor and the absence of TATA-box and CCAAT-box motifs typically present in eukaryotic polymerase II promoters.